In the field of respiratory devices, nebulizers are important devices used for the inhalation of drugs in the form of an aerosol to patients in need of a drug administered directly into the lungs. A nebulizer employs an apparatus that generates an aerosol or mist from a solution (usually an aqueous solution) or suspension of a drug. The mist may be an aerosolized suspension or an atomized suspension of drug, meaning micro-droplets suspended in air, medical oxygen, or other inhalable gas. The aerosol is conveyed to the mouth and/or nose of a patient and inhaled into the lungs. In some cases, the mist is conveyed to the lungs through a mouthpiece. In other cases, the nebulizer may be coupled to an inhalation mask.
Several nebulization technologies are known, including gas-jet, ultrasonic, and vibrating mesh nebulizers. This disclosure pertains to gas-jet nebulizers, which operate using a Venturi, wherein a jet of pressurized gas (air or other suitable gas, such as medical oxygen) is directed over an orifice on a capillary that is connected to a reservoir containing a drug in aqueous solution. The Venturi creates a localized low pressure zone that draws the drug solution out of the capillary orifice and into the air jet, where the liquid is atomized by a shearing effect. Typically, a baffle is employed in the jet effluent to assist in the formation of appropriate size droplets in the nebulized stream. In addition, a baffle prevents large droplets from exiting the device, so that only aerosol micro-droplets of drug containing solution exit the device. Still further, in many nebulizer designs, a baffle may be required to deflect the low pressure zone created by a Venturi jet over a liquid orifice in communication with the drug reservoir. In such designs, the baffle is required to draw the liquid into the stream of pressurized gas that causes nebulization of the liquid. An example of such a nebulizer is disclosed in U.S. Pat. No. 4,588,129. The aerosol is then inhaled by the patient. Typically, the aerosol production is continuous, so a vent is typically provided to ensure that the pressure differential created by the jet operates continuously and consistently. The drug reservoir in nebulizers is usually a cone, cup, or bowl-shaped vessel into which a sterile aqueous solution of the drug is added.
Other nebulizer methods besides gas-jet nebulizers are known, for example ultrasonic nebulizers and vibrating mesh nebulizers.
Typical drugs used with nebulizers are drugs for the treatment of asthma and obstructive pulmonary diseases, but other pulmonary and systematic medications may be administered by inhalation with nebulizers. For example, albuterol (called salbutamol in many countries), used for treating asthma and bronchospasm, may be administered as a nebulized solution. Another example is pentamidine, a drug used to treat Pneumocystis carinii pneumonia (PCP) (also called Pneumocystis jirovecii). Many other medications are useful or potentially useful as inhaled drugs and can potentially be used with a nebulizer.
Nebulizers are particularly useful for the administration of inhaled drugs to small children, elderly, unconscious, or disabled patients who cannot coordinate their breathing or take instruction on the use of coordinated inhalation devices, such as a metered dose inhaler. Also, nebulizers may be used with an inhalation mask for patients who cannot use a mouthpiece to inhale the drug. With a nebulizer, the dose of drug is administered to the patient over a period of several minutes, and possibly ten to twenty (or more) tidal or slow deep inhalations per minute, so breathing coordination is not required.
Nebulizers are typically equipped with a mouthpiece that a patient can insert in their mouth, making an airtight seal with their lips while inhaling through the mouth to ingest the nebulized medication into the lungs. In the case of patients who cannot hold a mouthpiece in their mouth or close their lips round the mouthpiece to create a seal, an inhalation mask may be used with a nebulizer. An example of such a mask is disclosed in PCT International Application WO 2012/173993.
In breath-actuated nebulizers, nebulization of the drug only occurs during inhalation by the patient. Breath-actuated nebulizers have a means for stopping the nebulization or flow of aerosol during exhalation or other intervals when the patient is neither inhaling or exhaling. Such devices are known, for example, from Denyer in U.S. Pat. RE40591, and Grychowski et al., in U.S. Pat. Nos. 5,823,179 and 6,644,304. A breath-actuated nebulizer has been marketed in the United States under the brand name AEROECLIPSE® by Monaghan Medical, and by Trudell Medical International in other countries.
Breath-actuated nebulizers may have significant advantages over conventional nebulizers. In conventional nebulizers, the drug is aerosolized continuously regardless of whether the patient is inhaling or not. Conventional nebulizers typically are vented to the atmosphere, so aerosol that is not inhaled is vented to the air in front of the patient. This wastes drug, and exposes others (including caregivers) in the vicinity to the aerosolized drug. In addition, the dosage is impossible to precisely determine because of this drug loss. In many cases, these shortcomings are not a problem, due to the low cost of conventional (continuous) nebulizers, and the low toxicity and low cost of drug of many of the drugs used in conventional nebulizers.
However, in the case of expensive drugs or drugs that may be toxic or sensitizing to others in the vicinity of the patient, conventional nebulizers are much less desirable than a breath-actuated nebulizer. With a breath-actuated nebulizer, the dosage can be precisely metered, and very little of the drug is wasted, since nebulization is stopped when the patient is not inhaling.